1. Field of the Invention
This invention relates in general to a method for fabricating a non-volatile memory and its operations, and more specifically relates to a method for fabricating an embedded flash ROM structure having code cells and data cells and operations for the same.
2. Description of Related Art
Generally, in a flash ROM array having memory cells having a insulating layer as a charge trapping layer, it usually comprises a code cell region and a data cell region. Each code cell can only store only one-bit data, and therefore its storage capacity is lower but high operation speed is its advantage. In contrast, two-bit data can be stored in each data cell, having the advantage of high storage capacity. The data cells are usually operated in a page program mode or a page read mode. However, if the data cells are operated in single read and program modes, it becomes slower.
As the foregoing description, the structure and the operation are different between the code cells and the data cells. For example, one data cell can store two bits while the code cell can only store one bit. Namely, the specification between the code and the data cells are different. Therefore, the present technology cannot provide a single process to manufacture a flash ROM structure having the code and the data cell regions at the same time because of their different specifications. In order to form a flash ROM structure having the code and the data cell regions, it requires two separated processes to form the code cell region and the data cell region respectively. Additionally, due to the operations of the code cell, it cannot use the process for making the data cell to form the code cell.
Therefore, according to the conventional technology, the manufacturing process for making the flash ROM structure having the code and the data cell regions becomes complex and the cost also increases. Furthermore, because two different processes are required to form such a structure above, the produce yield is reduced if some thing is wrong with the integration of the processes.